Three characters on the .org in the X-for-Y form. D4M reads as data for medicine, design for manufacturing, or dollars for mission.
Design for manufacturing is a real engineering discipline with its own literature and training. Data for medicine is a live institutional theme, covering health data research, patient registries, and the organisations working on making clinical data usable without compromising privacy. That sector is nonprofit and academic almost entirely, which matches the extension.
The 4-as-for convention supplies the grammar that makes three letters legible. Without it, D4M is a code. With it, it’s a purpose statement the reader completes themselves, and completed thoughts are remembered better than memorised strings.
Three characters fits on everything an organisation produces and never gets shortened into something someone else chose.
The name is listed for sale. Offers welcome.